Field of the Invention
The present invention relates to an organic light emitting display device and a method for manufacturing the same, and more particularly, to an organic light emitting display device which has a sufficient aperture ratio and is minimized in a voltage drop at a cathode and a method for manufacturing the same.
Description of the Related Art
An organic light emitting display device (OLED) is a self-light emitting display device that does not need a separate light source unlike a liquid crystal display (LCD). Thus, the OLED can be manufactured in a lightweight and thin form. Further, the OLED is advantageous in terms of power consumption since it is driven with a low voltage. Also, the OLED has an excellent color expression ability, a high response speed, a wide viewing angle, and a high contrast ratio (CR). Therefore, the OLED has received attention as a next-generation display device.
Among organic light emitting display devices, a top-emission organic light emitting display device uses a transparent electrode or a semi-transmission electrode as a cathode in order to emit light emitted from an organic light emitting layer to an upper side. In both instances, where a transparent electrode is used as a cathode and where a semi-transmission electrode is used as a cathode, the cathode is formed to have small thickness in order to improve transmissivity. A decrease in thickness of the cathode causes an increase in electrical resistance of the cathode. Thus, with a large-sized organic light emitting display device, voltage drop may occur in the pixels that are located farther away from a voltage supply pad unit, which may cause non-uniformity in luminance of the organic light emitting display device.
In the conventional OLED devices, auxiliary electrodes and partition walls provided on the same substrate as the cathode have been used to minimize the voltage drop. More specifically, a partition wall having a reverse tapered shape is provided between two adjacent sub-pixels and an auxiliary electrode is placed under the partition wall (i.e., toward the smaller surface of the auxiliary electrode). The partition wall functions similar to an umbrella, and hinders the organic light emitting layer to be disposed thereunder. As such, the partition wall disconnects the organic light emitting layer between the sub-pixel areas and exposes a portion of the auxiliary electrode without being covered by the organic light emitting layer. As such, the cathode over the organic light emitting layer, which has better step coverage than the organic light emitting layer, can be in contact with the exposed portion of the auxiliary electrode under the partition wall.
In such a configuration, the size of the contact area between the auxiliary electrode and the cathode depends on the size of the exposed portion of the auxiliary electrode. Not much benefit is gained from the auxiliary electrode if the contact area between the auxiliary electrode and the cathode is too small. Accordingly, the partition walls need to be sufficiently large in order to expose the auxiliary electrode. In a given size of the organic light emitting display device, however, increasing the size of the partition walls translates to a decrease in the aperture ratio of the sub-pixels of the organic light emitting display device.